This invention relates generally to the solids discharge handling apparatus associated with a reactor vessel system and, more specifically to that apparatus associated with a reactor vessel for the production of hypohalogenated acid by the mixing and reaction therein of an alkali metal hydroxide and a gaseous halogen. A preferred product acid is hypochlorous acid.
Hypochlorous acid is used extensively in the preparation of chlorohydrin and chloramines. Chloroisocyanurates are typical examples. Hypochlorous acid has been produced by several processes or techniques. The use of dilute hypochlorous acid and large quantities of halogen to produce hypohalites, such as sodium hypochlorite, is recent.
One technique employs the process in which chlorine, steam and air are bubbled through an aqueous solution of an alkali earth metal hypochlorite, such as calcium hypochlorite, to remove the resulting hypochlorous acid in vapor form. The hypochlorous acid is then condensed and stored for use. This process, however, produces a large volume of undesirable by-product, calcium chloride.
Another process uses a low concentration of aqueous caustic solution to scrub chlorine gas. However, the solution has an available chlorine content of about only 5% and, because of the chloride ion content, the hypochlorous acid that is formed quickly decomposes, most preferably to chloric acid.
Another related process prepares a solid mixture of alkali metal hypochlorite and alkali metal chloride by reacting chlorine gas with a spray of alkali metal hydroxide, while drying with a gas the reactants and product. Some cooling of the reacting chemicals and the drying gas may be done. The primary products of this process have very limited utility.
A more recent process, which produces hypochlorous acid vapor, sprays aqueous alkali metal hydroxide in droplet form or solid alkali metal hydroxide particles into gaseous chlorine. This approach attempts to utilize droplet sizes to attain the maximum surface to volume ratio possible. Droplets having an average diameter of less than about 1000 microns are employed.
These previous processes, and the apparatus employed to produce these processes, have suffered from not achieving substantially complete reactions between the chlorine and the alkali metal hydroxide. A critical factor in determining the complete reaction is the droplet size of the alkali metal hydroxide. It is also desirable that any hypochlorous acid produced and any water present be readily vaporizable. The salt particles produced as by-products in any process should be dry to facilitate handling and be continuously removable from the reaction while maintaining a seal to the atmosphere to prevent the gaseous product from escaping to the surrounding area and to prevent atmospheric gases from mixing with the gaseous product. The increased concentration of water and inert gases such as oxygen and nitrogen, in the reactor system when atmospheric gases intrude reduces the operating efficiency of the system. The salt particles should be sized so that they readily separate from the gaseous product mixture of hypochlorous acid.
Prior processes have produced oversized alkali metal hydroxide droplets that result in the undesired reaction of hypochlorous acid and the oversized particles to produce significant alkali metal chlorates. These oversized particles then retain excessive moisture so that caking results and the caked mass adheres to the reactor surfaces. These oversized particles can hamper the byproduct salt removal additionally. The presence of such alkali metal chlorates reflect reduced yields of the desired hypochlorous acid, while increasing the raw material and operating costs. Lastly, the presence of halogen gas in the porous solid by-product salt can cause the salt to clump or bind together, thereby plugging the salt handling apparatus.
These problems are solved in the design of the present invention wherein by-product salt handling apparatus is provided for a reactor vessel for the production of a hypohalogenated acid in which the mixing and reaction of alkali metal hydroxide and a gaseous halogen occurs.